1. Field of the Invention
This invention relates to a miniature circuit breaker, and more particularly, to a molded case having a base and a cover designed to provide equal strength in the base and in the cover for optimum overall strength which becomes important when a short circuit occurs; full handle member support in the base for easy assembly of the circuit breaker; and a reduced overall thickness for the base and cover assembly.
2. Background Information
Present designs for a molded case for a miniature circuit breaker take various forms for accommodating the handle part of an operating mechanism for the circuit breaker. One such design for a molded case provides for a base whose peripheral walls are relatively wide accounting substantially for the overall thickness of the assembled molded case, and the cover is relatively thin accounting very little for the overall thickness of the assembled molded case. In this molded case design, the handle part is substantially supported in an aperture formed in the base which may allow for easy assembling of the components in the base of the circuit breaker. However, under some conditions, the relatively thin cover may have a tendency to break away from the base or fly off of the base when a short circuit or an overcurrent occurs due to the buildup of gas pressure in the molded case.
A further design for a molded case for a miniature circuit breaker of the prior art involves a base and a cover whose peripheral walls have substantially equal widths, whereby the handle part of the operating mechanism is supported equally in both the base and in the cover. In this design, part of the aperture for the handle part is in the base, and part of the aperture is in the cover. This makes assembling of the components for the circuit breaker mechanism, comprising a handle part, a cradle, a spring, and a contact arm, somewhat difficult in that the spring biased handle part tends to cock and if the handle bearing is not completely in place in the base, which normally happens in this type of molded case design, the components pop out of the base. This design also does not provide close enough tolerances between the handle and the assembled molded case to prevent the flame and hot gases from escaping when an arc interruption occurs. This design has structural limitations in that if the tolerances were made any closer, the bearing on the handle part would rub with the other parts of the assembled case.
Both these prior art molded case designs are generally about 1.00 inch thick in assembled form and may be adequate for certain installations and amperage interruption requirements, but do not allow the overall thickness of the molded case to be minimized and still provide the strength and integrity for a relatively thin, single pole miniature circuit breaker.
There remains a need, therefore, for an improved case design for a miniature circuit breaker whereby the overall thickness of the assembled molded case can be even less than previously, including an improved aperture design for the handle part.
There also remains a need for an improved case design which is relatively thinner than the previous molded case design and which provides the strength and integrity for a single pole miniature circuit breaker.
And still further, there remains a need for an improved case design for a miniature circuit breaker which provides ease in assembly of the components of the circuit breaker in the base.